Groundwater Legislation Update

In September, Governor Jerry Brown signed The Sustainable Groundwater Management Act of 2014 (SGMA). The SGMA is a comprehensive three bill package that includes AB 1739 (Dickinson), SB 1168 (Pavely) and SB 1319 (Pavely). From MID’s perspective, the SGMA sets the framework for statewide sustainable groundwater management by local agencies. The SGMA requires, among other items, the formation of Groundwater Sustainability Agencies (GSA) and the preparation of Groundwater Sustainability Plans (GSP) with a focus on long-term sustainability in the sub-basin.

As you know, MID has been actively engaged in sustainable groundwater management within our irrigation service area for more than 20 years. We will continue to represent your best interests through a multitude of local groundwater organizations and we are optimistic that through State law and the continued cooperation of local water purveyors we will bring careful, deliberate and coordinated action to continued groundwater sustainability moving forward. If you have any questions or concerns, please email us at strgba@mid.org or visit our website at www.strgba.org.

The Sustainable Groundwater Management Act of 2014 (PDF)
Fact Sheet - Sustainable Groundwater Management (PDF)
Frequently Asked Questions - Sustainable Groundwater Management (PDF)

Groundwater in the Modesto Irrigation District

Water that is found beneath the surface of the Earth in saturated rock formations is called groundwater.  It is a very important and valuable water supply for much of the world and particularly in the Central Valley of California.  Groundwater is poorly understood yet represents a very significant component of our overall water supply.  In fact, many of the cities in the Central Valley rely 100% on groundwater for their drinking water supply, as did the City of Modesto for most of its history.

According to information contained in  California Department of Water Resources Bulletin 118, the estimated amount of groundwater stored within the Modesto Subbasin, in just 100 feet of saturated thickness, is 5 million acre feet or 2.5 times greater than the maximum storage capacity of Don Pedro Reservoir.  The Modesto Subbasin is defined as that area of land lying between the Stanislaus River on the north, the Tuolumne River on the south, the Sierra Nevada Mountain foothills on the east and the San Joaquin River on the west.  The MID water service boundary is entirely located within the Modesto Subbasin.  The primary source of recharge (60%) in the basin occurs through agricultural  irrigation using surface water supplied by the MID.  Other sources of recharge in the basin occur via rainfall and seepage from surface water bodies such as Modesto Reservoir.  Some reaches of the Tuolumne River are supplemented with groundwater inflows.

 MID Operations – Conjunctive Use 

• MID owns and operates more than 100 water wells.  About half of these are used for water table control on the west side of the MID water service area where there is a high water table.  Without being able to control the elevation of the water table via pumping from shallow wells the soil conditions would be waterlogged and crops would not be able to be grown.
• The remaining 50 or so wells are deeper production wells that are used to supplement the surface water supply in the canal distribution system.  Most of these deeper wells are located immediately adjacent to the canal system in MID-owned rights-of-way.
• MID pumps on an average annual basis about 38,000 acre feet.
• These facilities are replaced and/or upgraded on an ongoing basis at the rate of three replacement/upgrades per year. 

Modesto Regional Water Treatment Plant

•  The loss of recharge that has occurred due to the conversion from agricultural to urban land use (almost 28,000 acres over the last 60 years) and the ensuing increase in urban demand (met by groundwater) resulted  in an continually expanding and deepening groundwater “cone of depression” in the Modesto urban area.
• That adverse effect, in part, led to the planning and ultimate construction of the Modesto Regional Water Treatment Plant (MRWTP), owned and operated by MID.  Phase 1 of the MRWTP, completed in 1994, supplies more than 30 million gallons per day (mgd) to the City of Modesto (roughly 50% of the annual average demand).  The resulting relaxation of groundwater withdrawals by the City allowed groundwater levels to recover by more than 40 feet in the local urban area.
• Phase Two of the MRWTP (an additional 30 mgd) is presently under construction.

Proactive Management

• It’s critical for local agencies to cooperate when managing water resources.  Piecemeal efforts just don’t work.  To address this need, the STRGBA (Stanislaus & Tuolumne River Groundwater Basin Association, represented by the cities of Modesto, Oakdale and Riverbank, Stanislaus County, Oakdale Irrigation District and the Modesto Irrigation District) was formed.  MID is leading the effort to manage groundwater quantity and protect groundwater quality in the region and throughout the basin as demonstrated by the following programs and projects.
• MID is now accepting applications for the Long-Term Groundwater Replenishment Program. View the application and learn more about the program here.

Integrated Regional Groundwater Management Plan

• The plan, adopted in 2005, encourages local agencies to work cooperatively, takes a basin-wide (regional) approach, is based on a solid body of scientific data, and will be refined and updated over time.
• The plan’s goal is to protect the quantity and quality of groundwater resources through the development and implementation of Basin Management Objectives.

The U.S. Geological Survey (USGS) is conducting a thorough, multi-phased study of the Modesto Groundwater Sub-Basin.  The first phase of this study resulted in a document titled “Hydrogeologic Characterization of the Modesto Area, San Joaquin Valley, California.”  One of the key findings of this report is that the primary means of recharge in the Modesto Subbasin is via the application of surface water for agricultural irrigation purposes.  Ultimately the USGS evaluation will:

• Create a scientific toolkit that local agencies can use to make wise choices about water management and land use.
• One tool will be a predictive 3-D computer model of the groundwater basin.
  •  Let’s say a water manager plans to drill 15 new wells. Before putting that plan into action, he can use the model to test his plan and forecast the results.
  • Another example:  Where are the best areas and methods for achieving  groundwater recharge?
• The model is to be completed and made available by the end of 2012.

Wellfield Optimization Project

• A separate study took a look at how MID can get the greatest benefit out of its own water wells in concert with surface water, under both dry and wet conditions.   This resulted in the Wellfield Optimization Decision Support System and was paid for under a grant that MID received under the umbrella of the STRGBA.

Recharge Mapping

• Another study that was performed for STRGBA was the mapping of the zones of recharge within the Modesto Subbasin.
• The resulting maps show that the areas with the greatest recharge occur primarily to the north and east of the City of Modesto, and in the area surrounding Modesto Reservoir.
• This study was performed under the guidance of DWR via a local assistance program and at no cost to any of the agency members of STRGBA.

• Recharge Characterization for Stanislaus and Tuolumne Rivers Groundwater Basin
• Hydrogeologic Characterization of the Modesto Area, San Joaquin Valley, CA.
• Integrated Groundwater Management Plan for the Modesto Subbasin
• Modesto Basin Contour Map